The EU Water Framework Directive (WFD) requires river assessment systems based on benthic invertebrates. The AQEM project is developing, at a European scale, such a methodology, based on a comparison of communities of reference streams and degraded streams. The project is focussing on three main impact types: morphological degradation, organic pollution and acidification. This paper presents the outline of the AQEM project with special emphasis on: -an overview of assessment systems with benthic invertebrates presently applied in Europe -an overview of stream typology approaches in Europe -the selection process of the stream types investigated in AQEM -the criteria used to select reference sites -the design of the sampling programme -the microhabitat-based sampling method applied in AQEM -the links and possibilities of integration between AQEM and existing assessment systems.

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